Fume hoods are employed in laboratories and other locations where technicians work with materials that generate dangerous or noxious contaminants. Conventional fume hoods include an enclosed chamber in which work is performed. An access opening is provided in the front of the chamber through which a technician can perform work within the chamber. An exhaust system is configured to exhaust air and contaminants from the chamber to a location outside the fume hood. The exhaust system draws air flow through the access opening and out of the chamber. This inward flow of air is intended to prevent contaminants from exiting the chamber through the access opening.
FIG. 1 illustrates a typical conventional fume hood 10. The illustrated fume hood 10 includes a cabinet 12 having a work chamber 14. The chamber 14 includes a flat bottom floor (surface) 16 on which work is performed within the chamber 14 and an access opening 18 at the front of the chamber 14. A sash 20 is mounted in the cabinet 12 for up and down movement in a vertical plane to open and close the access opening 18. The sash 20 is conventionally formed of transparent material, such as glass, to permit viewing of the chamber 14 therethrough.
An average face velocity of about 100 feet per minute (fpm) or greater at the access opening of a fume hood is stipulated by California regulations (CAL-OSHA) in order to prevent harmful contaminants from escaping the chamber through the access opening. This average face velocity of about 100 fpm is also becoming the traditional industry and facility standard. Unfortunately, such an air velocity and resultant air volumes may result in the withdrawal of an equivalent amount of air from the room in which a fume hood is located. Since the supply air in most laboratories is heated and cooled and is 100% outdoor air, it is desirable to reduce the amount of conditioned air that is drawn through the fume hoods. It is estimated by some that the cost of moving conditioned air (i.e., heated and cooled air) drawn through a conventional fume hood may exceed $5,000 per year.